In recent years, using materials containing CNTs, materials having functions such as an anti-electrostatic property, electrical conductivity, thermal conductivity and an electromagnetic wave shielding property have been actively developed. For example, many studies regarding a composite material having functions such as an anti-electrostatic property, electrical conductivity, thermal conductivity and an electromagnetic wave shielding property, and a laminate obtained by laminating these composite materials have been performed by using a polymer such as a polyamide, a polyester, a polyether or a polyimide, or an inorganic material such as glass or a ceramic material as a matrix, and dispersing a CNT in the matrix.
As a CNT, there are a monolayer nanotube consisting of one graphene layer, and a multilayer nanotube constructed of a plurality of graphene layers. To utilize structural properties such as an extremely great aspect ratio and an extremely small diameter, and to manifest transparency, electrical conductivity and other physical properties, it is necessary to finely disperse CNTs at an extremely high level, ultimately, to monodisperse CNTs. Particularly, when the composite material is laminated on other materials, it is necessary to finely disperse a CNT in the composite material at a necessary minimum amount and at a high level so as not to give any influence on optical properties of the other materials.
In addition, to utilize properties of a CNT by coating, it is necessary to form a network structure of a finely dispersed CNT on a substrate. Thereby, it is expected that high transparency and electrical conductivity can be manifested even when the use amount of a CNT is extremely small.
Previously, processes for manufacturing an electrically conductive film by a method of applying an electrically conductive layer containing a CNT on a film, or the like, have been known. However, in these known techniques, for example, in JP-A No. 2002-67209, a coated film thickness should become extremely great to impart desired electrical conductivity, neglecting processability and transparency as an electrically conductive substrate. In addition, in JP-A No, 2004-195678, a conjugated polymer-based electrically conductive polymer is used as a binder resin to maintain electrical conductivity of a CNT in an electrically conductive layer, but an electrically conductive property which is originally possessed by a CNT is not utilized, and a resistance value as an electrically conductive film is extremely high. In JP-A No. 2007-112133, a production process of an electrically conductive film is complicated to exert an electrically conductive property of a CNT, and there is a problem in productivity and economy. Also in Japanese Patent No. 3665969, to improve an adhesion property between an electrically conductive layer and a substrate, a CNT is applied and, thereafter, the product is overcoated with a binder resin, and there is a problem in productivity and economy as in JP-A No. 2007-112133. In addition, since an organic solvent is used as a solvent in the four patent documents shown herein, it cannot be said to be optimal also in respect of environmental load. Further, for use as an electrostatic film or a transparent electrically conductive film as an electrically conductive layer containing a CNT, solvent resistance and abrasion resistance of an electrical conductive layer are important, but these properties are not referred to in the four patent documents, and there is a fear of deficiency in solvent resistance and abrasion resistance.
Also, a CNT has been dispersed in a matrix or a resin to manufacture a laminate in which a CNT is finely dispersed. However, the dispersed state of a CNT is not necessarily good and, in lamination by previous coating, it was difficult to manifest properties inherent to a CNT since a binder resin hinders electrical conductivity of a CNT, or a CNT causes aggregation in a drying step. In addition, abrasion resistance and solvent resistance were not sufficient.
It could therefore be helpful to provide an electrically conductive film excellent in transparency, electrical conductivity, abrasion resistance, and solvent resistance, and having a coated film (electrically conductive layer) in which a CNT is finely dispersed, at a lower cost than the previous manufacturing cost.